The invention relates to a femur slide comprising two convex curved condyle cups which are anteriorly rigidly joined by a patella shield.
Femur slides of this type are generally known. In this respect, reference is made, for example, to DE 40 41 920 C2 or WO 87/02882.
In present day operation techniques for knee-joint replacement on the femur, the implant is aligned at the rear or posterior condyles. An equal amount of bone is removed from both condyles. The anterior or central cut lies parallel to the posterior or dorsal cut and thus to the posterior condyle edge. However, this has a disadvantage for various technical and anatomical reasons in that firstly the rotational axis no longer coincides with the axis offered by the side bands and secondly the implant is, due to the non-anatomical position in the curvature, seated either too tightly on the medial side or too loosely on the lateral side.
For this reason, experts in knee-joint endoprosthetics recommend an outward rotation for the condyles. The orientation is served either by the so-called epicondyle axis or the so-called xe2x80x9cwhitesidexe2x80x9d line. Due to this outside rotation of the cutting instruction, laterally less bone relative to the medial side is removed in the posterior area. At the same time, more bone is resected anterio-laterally as compared to the medial side. However, as the implants are matched to the original cutting line which is characterized by equal material thickness medially and laterally, a higher buildup results on the lateral side which compensates the undesirable play on the lateral side in the curvature. At the same time, the outside rotation of the implant laterally offsets the patella socket which reduces the danger of patella subluxations. However, this process presents the following disadvantages:
The anterio-lateral edge of the implant often protrudes over the bone edge;
due to lower cut orientation on the lateral side, the anterior cortex is often cut into which is undesirable for various reasons;
the patella shield of the implant protrudes on the medial side over the bone, i.e. a gap remains between shield and bone. The reason for this lies in the natural geometry of the anterior femur which is medially slanted in the distal area.
It is an object of the present invention to make available a femur slide by means of which advantages of the conventional cuts at the distal end of the femur can be maintained, in which in particular the saw cuts can be better matched to the anatomy of the femur whilst at the same time achieving a kinematically optimal position of the implant with outside rotation.
An object of the invention involves a femur slide having a patella shield and two convex curved condyle cups which are anteriorly rigidly joined by the patella shield. The two condyle cups and the patella shield define internally anterior and posterior matching surfaces which correspond with a femural ventral cut and with a femural dorsal cut. Relative to a reference plane which is defined by posterior slide surfaces of the condyle cups, an anterio-medial matching surface lies nearer to the reference plane than an anterio-lateral matching surface. The anterior matching surfaces are defined by a slanted surface with is continuously slanted in a direction from lateral to medial to posterior, and an angle between the slanted surface and the reference plane lies between three and ten degrees.
Thus, the basic idea of the present invention lies in rotating the anterior or ventral cut in the transversal plane. In a preferred arrangement, the dorsal cut remains parallel to the condyles or parallel to the plane defined by the posterior slide surfaces of the condyle cups. In particular the thickness of the dorsal condyle cups shall be medially and laterally equal in a further preferred arrangement.
The inventive structure achieves anatomical matching, and it is left to the surgeon to position the precise amount of rotation intraoperatively and in dependence of the individual anatomy.